The present invention relates to a method of producing a ceramic honeycomb structural body having a cordierite composition by means of an extrusion molding, and particularly relates to a method suitable for producing a ceramic honeycomb structural body having a thin wall thickness of 50 xcexcm or less.
Generally, various methods for producing a honeycomb structural body having a cordierite composition by means of an extrusion molding using a molding die are known. In all the known methods, a predetermined ceramic honeycomb structural body is produced by mixing predetermined ceramic raw materials, adding a forming agent and water to the resultant mixture to obtain a batch for forming, and extruding the batch through the molding die. The molding die used here comprises a plurality of batch supply holes arranged at a batch supply side thereof and slits communicating with the batch supply holes arranged at a batch discharge side thereof. Therefore, the slit defines a wall thickness of the honeycomb structural body.
When the ceramic honeycomb structural body is produced by means of the extrusion molding according to the known producing method, and, particularly when the ceramic honeycomb structural body having a thin wall is produced by means of the extrusion molding, if a raw material particles larger than the wall thickness of the ceramic honeycomb structural body to be formed is included in the ceramic raw materials, the raw material particle is stuck for the slit of the molding die, and thus defects occur at a corresponding portion of the ceramic honeycomb structural body after the extrusion molding. Therefore, coarse particles are generally removed from the raw materials in consideration of the wall thickness of the ceramic honeycomb structural body to be formed by means of the extrusion molding.
As the coarse particle removing process from the ceramic raw materials, use is made of an air elutriation using for example Alpine type classifier for the wall thickness of 150 xcexcm or more, and further use is made of for example a centrifugal type classifier for the wall thickness of 50 xcexcm or more. However, in the air elutriation using Alpine type classifier, there is a drawback that raw material particles are agglutinated. Moreover, in the case of using the centrifugal type classifier, there is a drawback that an industrially available sieve is a mesh of 45 xcexcm. Therefore, in order to extrude the ceramic honeycomb structural body having the wall thickness of 50 xcexcm or less that is highly required in a recent year, it is not possible to use the air elutriation process or the centrifugal type classifier as mentioned above. In addition, in the case of classifying the raw materials, a miss classification surely occurs. That is to say, if the raw materials are classified by using a centrifugal type sieve having a mesh of 45 xcexcm, the coarse particle larger than 45 xcexcm are not always removed. Therefore, use is experimentally made of a sieve having a mesh 10% or more smaller than a slit width of the die using for the extrusion molding of the honeycomb structural body to be formed.
An object of the invention is to eliminate the drawbacks mentioned above and to provide a method for producing a ceramic honeycomb structural body which can prevent an agglutination of raw material particles and which can remove coarse raw material particles effectively.
According to a first aspect of the invention, a method for producing a ceramic honeycomb structural body, comprises the steps of: providing raw materials for forming a cordierite composition; preparing slurries of respective raw materials to obtain raw material slurries respectively; slowing the thus obtained raw materials slurries to pass through a sieve having a mesh of 45 xcexcm or less; subjecting the raw material slurries, that are passed through the sieve, respectively to spray drying to prepare raw material powders; mixing the thus prepared raw material powders to obtain a mixture having a cordierite composition; adding a forming agent and water to the thus obtained mixture to obtain a batch for forming; and subjecting the thus obtained batch for forming to an extrusion molding to obtain a honeycomb structural body having a wall thickness of 50 xcexcm or less.
Moreover, according to a second aspect of the invention, a method for producing a ceramic honeycomb structural body, comprises the steps of: providing a mixture of raw materials for forming a cordierite raw material slurry; allowing the thus obtained cordierite raw material slurry to pass through a sieve having a mesh of 45 xcexcm or less; subjecting the cordierite raw material slurry, that are passed through the sieve, to spray drying to prepare raw material powders; adding a forming agent and water to the thus prepared raw material powders to obtain a batch for forming; and subjecting the thus obtained batch for forming to an extrusion molding to obtain a honeycomb structural body having a wall thickness of 50 xcexcm or less.
Further, according to a third aspect of the invention, a method of producing a ceramic honeycomb structural body, comprises the steps of: providing a mixture of raw materials for forming a cordierite composition; preparing a slurry of the mixture to obtain a cordierite raw material slurry; allowing the thus obtained cordierite raw material slurry to pass through a sieve having a mesh of 45 xcexcm or less; dissolving methyl cellulose and slip additives into the cordierite raw material slurry, that are passed through the sieve, as forming agents; subjecting the cordierite raw material slurry into which the forming agents are dissolved to filter pressing to obtain a batch for forming having a predetermined water amount; and subjecting the thus obtained batch for forming to obtain a honeycomb structural body having a wall thickness of 50 xcexcm or less.
In the present invention, the raw materials for forming a cordierite composition are dissolved into water with an dispersing agent to prepare a slurry, and the thus prepared slurry is passed through the sieve having a mesh of 45 xcexcm or less. After that, the slurry after sieving is dried by means of the spray drying to obtain dry powders, and the batch for forming is obtained by using the dry powders. Or, the batch for forming is obtained by the filter pressing. That is to say, the batch for forming is obtained by using the raw material powders which are passed through the sieve in a wet state. Therefore, it is possible to prevent agglutination of the raw material particles and to remove the coarse raw material particles effectively. As a result, if the extrusion molding is performed by using the thus obtained batch for forming, it is possible to form the ceramic honeycomb structural body having an extremely thin wall thickness with no defects.